Dynamic cardiocirculatory control during propofol anesthesia in mechanically ventilated patients

Bradyarrhythmia and hypotension during anesthetic induction-reconsideration of nifedipine: a case report

Cardiac events sometimes occur during anesthesia and surgery and may be severe or even life-threatening. This report describes a case of severe bradyarrhythmia during anesthetic induction with propofol, midazolam, sufentanil, and vecuronium. The patient took nifedipine sustained-release tablets on the morning of surgery as routine treatment for hypertension, and this medication may have contributed to the bradyarrhythmia. Nifedipine is a calcium channel blocker that can dilate blood vessels, depress the activity of the sinoatrial node, and delay the conduction of the atrioventricular node. Although these effects are not usually significant, they may be enhanced by anesthetics or other concomitant drugs. For patients of advanced age, especially those with autonomic disturbance or cardiac abnormalities, these effects can be remarkable, and discontinuation of nifedipine should be considered.

A comparison of the efficacy of three different peak airway pressures on intraoperative bleeding point detection in patients undergoing thyroidectomy: a randomized, controlled, clinical trial

BACKGROUND

Various techniques are used to detect intraoperative bleeding points in thyroid surgery. We aimed to assess the effect of increasing peak airway pressure to 30, 40 and 50 cm H₂O manually in detecting intraoperative bleeding points.

METHODS

One hundred and 34 patients scheduled for total thyroidectomy were included to this prospective randomised controlled clinical study. We randomly assigned patients to increase peak airway pressure to 30, 40 and 50 cm H₂O manually intraoperatively just before surgical closure during hemostasis control. The primary endpoint was the rate of bleeding points detected by the surgeon during peak airway pressure increase.

RESULTS

The rate of detection of the bleeding points was higher in 50 cm H₂O Group than the other two groups (15.9 vs 25.5 vs 40%, P = 0.030), after pressure administration, the HR, SpO₂, and P peak were similar between groups (P = 0.125, 0.196, 0.187, respectively). The median duration of the bleeding point detection after the pressure application was 21.82 s in 30 cm H₂O, 25 s in 40 cm H₂O, and 22.50 s in 50 cm H₂O groups. Postoperative subcutaneous hematomas or hemorrhages requiring surgery were not seen in any patient.

CONCLUSIONS

Manually increasing peak airway pressure to 50 cm H₂O during at least 22.50 s may be used as an alternative way to detect intraoperative bleeding points in thyroid surgery.

CLINICAL TRIAL REGISTRATION

NCT03547648. Registered 6 June2018.

Propofol protects human cardiac cells against chemical hypoxiainduced injury by regulating the JNK signaling pathways

Propofol is a widely used intravenous anesthetic shown to exert a cardioprotective role against oxidative stress and ischemia/reperfusion injury in rat cardiac H9c2 cells. However, the regulatory mechanisms and functions of propofol in human cardiomyocytes remain unknown. The present study chemically induced hypoxia with cobalt chloride (CoCl₂) to mimic cardiomyocyte ischemic injury in human cardiac AC16 and HCM cells. To investigate its underlying mechanisms, propofol was added to the cells before the chemical hypoxia phase. The present results suggested that, in response to hypoxia, mitochondrial membrane potential was lost, and cardiomyocyte viability and superoxide dismutase levels decreased. However, the present results showed that reactive oxygen species and malondialdehyde levels increased. The present results suggested that these effects were significantly reversed following propofol treatment. Additionally, the present results suggested that the protective effect of propofol against CoCl₂-induced injury may be inhibited by the activation of the JNK signaling pathways. The present results indicated that propofol pre-treatment inhibited CoCl₂-induced myocardial injury by preventing mitochondrial dysfunction, which may be partially due to the activation of the JNK signaling pathways. Therefore, propofol may exert anti-oxidative effects in human cardiac cells. The present results suggested that propofol may be used as a treatment for oxidative stress-related cardiac disorders.

Multiscale Decomposition of Cardiovascular and Cardiorespiratory Information Transfer under General Anesthesia

The analysis of short-term cardiovascular and cardiorespiratory regulation during altered conscious states, such as those induced by anesthesia, requires to employ time series analysis methods able to deal with the multivariate and multiscale nature of the observed dynamics. To meet this requirement, the present study exploits the extension to multiscale analysis of recently proposed information decomposition methods which allow to quantify, from short realizations, the amounts of joint, unique, redundant and synergistic information transferred within multivariate time series. These methods were applied to the spontaneous variability of heart period (HP), systolic arterial pressure (SAP) and respiration (RESP) in patients undergoing coronary artery bypass graft monitored before and after the induction of general anesthesia. We found that, after anesthesia induction, information is processed within the cardiovascular network in a scale-dependent way: at short time scales, a shift from synergistic to redundant information transferred from SAP and RESP to HP occurs, which is associated with enhanced baroreflex-mediated respiratory effects on arterial pressure; at longer time scales, the increased information transfer from SAP to HP denotes an enhancement of the baroreflex coupling related to slow cardiovascular oscillations.

Effects of propofol anesthesia induction on the relationship between arterial blood pressure and heart rate

This paper presents the analysis of autonomic nervous system (ANS) control of heart rate (HR) and of cardiac baroreflex sensitivity (BRS) in patients undergoing general anesthesia for major surgery through spectral analysis techniques and with the Granger causality approach that take into account the causal relationships between HR and arterial blood pressure (ABP) variability. Propofol produced a general decrease in ABP due to its vasodilatory effects, a reduction in BRS, while HR remained unaltered with respect to baseline values before induction of anesthesia. The bivariate model suggests that the feedback pathway of cardiac baroreflex could be blunted by propofol induced anesthesia and that the feedforward pathway could be unaffected by anesthesia.

Baroreflex sensitivity variations in response to propofol anesthesia: comparison between normotensive and hypertensive patients

The aim of this paper is to compare baroreflex sensitivity (BRS) following anesthesia induction via propofol to pre-induction baseline values through a systematic and mathematically robust analysis. Several mathematical methods for BRS quantification were applied to pre-operative and intra-operative data collected from patients undergoing major surgery, in order to track the trend in BRS variations following anesthesia induction, as well as following the onset of mechanical ventilation. Finally, a comparison of BRS trends in chronic hypertensive patients (CH) with respect to non hypertensive (NH) patients was performed. 10 NH and 7 CH patients undergoing major surgery with American Society of Anesthesiologists classification score 2.5 ± 0.5 and 2.6 ± 0.5 respectively, were enrolled in the study. A Granger causality test was carried out to verify the causal relationship between RR interval duration and systolic blood pressure (SBP), and four different mathematical methods were used to estimate the BRS: (1) ratio between autospectra of RR and SBP, (2) transfer function, (3) sequence method and (4) bivariate closed loop model. Three different surgical epochs were considered: baseline, anesthetic procedure and post-intubation. In NH patients, propofol administration caused a decrease in arterial blood pressure (ABP), due to its vasodilatory effects, and a reduction of BRS, while heart rate (HR) remained unaltered with respect to baseline values before induction. A larger decrease in ABP was observed in CH patients when compared to NH patients, whereas HR remained unaltered and BRS was found to be lower than in the NH group at baseline, with no significant changes in the following epochs when compared to baseline. To our knowledge, this is the first study in which the autonomic response to propofol induction in CH and NH patients was compared. The analysis of BRS through a mathematically rigorous procedure in the perioperative period could result in the availability of additional information to guide therapy and anesthesia in uncontrolled hypertensive patients, which are prone to a higher rate of hypotension events occurring during general anesthesia induction.

Estimation of baroreflex sensitivity during anesthesia induction with propofol

This paper presents the analysis of the autonomic nervous system (ANS) control and cardiac baroreflex sensitivity in patients undergoing general anesthesia for major surgery, with the goal of evaluating the effects of anesthesia bolus induction with propofol on autonomic control of heart rate (HR) and arterial blood pressure (ABP). The increase in baroreflex gain in the LF band observed through two different methods hints at the fact that the baroreflex may increase heart period (HP) following a transient ABP decrease, but its response displays a larger amplitude, to compensate for the blunting of the sympathetic action on heart rate and vascular resistance.

Transfer function analysis of baroreflex function in a rabbit model of endotoxic shock

Sepsis is characterized by profound cardiovascular abnormalities which may result from the derangements in the arterial baroreflex system and other autonomic regulatory functions. In this study, a mechanically ventilated and anesthetized rabbit model of endotoxic shock was utilized to mimic the behaviors of the cardiovascular system in a sepsis patient. 13 adult New Zealand white rabbits were studied, with 8 of them injected with endotoxin and the remaining given saline solution as sham fluid. Measurements of heart period (RRi) and systolic blood pressure (SBP) were obtained pre-and post-intervention after a 90 minute period, which allowed spectral and cross-spectral analysis of heart rate and blood pressure variabilities to be performed. A significant increase of blood lactate level (p < 0.01) in post-intervention stage signified the onset of distributive shock. Based on this model, the novel findings were that in the low frequency (LF) and mid frequency (MF) bands, there was a decrease in coherence (p < 0.01 and p < 0.05 respectively) and loss of phase delay (p < 0.05) between SBP and RRi, along with a depression in transfer function gain in the LF band (p < 0.05), which might indicate an impairment of baroreflex control of heart rate following the administration of endotoxin. None of the above variables changed significantly in the control group. Moreover, endotoxin also led to a decrease in RRi variability in the ventilatory frequency (VF) band, suggesting a suppression of cardiac vagal modulation. These results highlight the potential value of frequency spectrum analysis combined with transfer function analysis of cardiovascular variability in the assessment of autonomic and baroreflex-related changes associated with endotoxic shock.

Changes in pulse pressure variability during cardiac resynchronization therapy in mechanically ventilated patients

INTRODUCTION

The respiratory variation in pulse pressure (PP) has been established as a dynamic variable of cardiac preload which indicates fluid responsiveness in mechanically ventilated patients. The impact of acute changes in cardiac performance on respiratory fluctuations in PP has not been evaluated until now. We used cardiac resynchronization therapy as a model to assess the acute effects of changes in left ventricular performance on respiratory PP variability without the need of pharmacological intervention.

METHODS

In 19 patients undergoing the implantation of a biventricular pacing/defibrillator device under general anesthesia, dynamic blood pressure regulation was assessed during right ventricular and biventricular pacing in the frequency domain (power spectral analysis) and in the time domain (PP variation: difference between the maximal and minimal PP values, normalized by the mean value).

RESULTS

PP increased slightly during biventricular pacing but without statistical significance (right ventricular pacing, 33 +/- 10 mm Hg; biventricular pacing, 35 +/- 11 mm Hg). Respiratory PP fluctuations increased significantly (logarithmically transformed PP variability -1.27 +/- 1.74 ln mm Hg2 versus -0.66 +/- 1.48 ln mm Hg2; p < 0.01); the geometric mean of respiratory PP variability increased 1.8-fold during cardiac resynchronization. PP variation, assessed in the time domain and expressed as a percentage, showed comparable changes, increasing from 5.3% (3.1%; 12.3%) during right ventricular pacing to 6.9% (4.7%; 16.4%) during biventricular pacing (median [25th percentile; 75th percentile]; p < 0.01).

CONCLUSION

Changes in cardiac performance have a significant impact on respiratory hemodynamic fluctuations in ventilated patients. This influence should be taken into consideration when interpreting PP variation.

Propofol for sedation in neuro-intensive care

Interventions in the intensive care unit often require that the patient be sedated. Propofol is a widely used, potent sedative agent that is popular in critical care and operating room settings. In addition to its sedative qualities, propofol has neurovascular, neuroprotective, and electroencephalographical effects that are salutory in the patient in neurocritical care. However, the 15-year experience with this agent has not been entirely unbesmirched by controversy: propofol also has important adverse effects that must be carefully considered. This article discusses and reviews the pharmacology of propofol, with specific emphasis on its use as a sedative in the neuro-intensive care unit. A detailed explanation of central nervous system and cardiovascular mechanisms is presented. Additionally, the article reviews the literature specifically pertaining to neurocritical care use of propofol.

Distinct molecular targets for the central respiratory and cardiac actions of the general anesthetics etomidate and propofol

General anesthetics are among the most widely used and important therapeutic agents. The molecular targets mediating different endpoints of the anesthetic state in vivo are currently largely unknown. The analysis of mice carrying point mutations in neurotransmitter receptor subunits is a powerful tool to assess the contribution of the respective receptor subtype to the pharmacological actions of clinically used general anesthetics. We examined the involvement of beta3-containing GABA(A) receptors in the respiratory, cardiovascular, hypothermic, and sedative actions of etomidate and propofol using beta3(N265M) knock-in mice carrying etomidate- and propofol-insensitive beta3-containing GABA(A) receptors. Although the respiratory depressant action of etomidate and propofol, as determined by blood gas analysis, was almost absent in beta3(N265M) mice, the cardiac depressant and hypothermic effects, as determined by radiotelemetry, and the sedative effect, as determined by decrease of motor activity, were still present. Taken together with previous findings, our results show that both immobilization and respiratory depression are mediated by beta3-containing GABA(A) receptors, hypnosis by both beta3- and beta2-containing GABA(A) receptors, while the hypothermic, cardiac depressant, and sedative actions are largely independent of beta3-containing GABA(A) receptors.